docs: def Suratman(L, rho, mu, sigma):
      r'''Calculates Suratman number, `Su`, for a fluid with the given
      characteristic length, density, viscosity, and surface tension.
  
      .. math::
          \text{Su} = \frac{\rho\sigma L}{\mu^2}
  
      Parameters
      ----------
      L : float
          Characteristic length [m]
      rho : float
          Density of fluid, [kg/m^3]
      mu : float
          Viscosity of fluid, [Pa*s]
      sigma : float
          Surface tension, [N/m]
  
      Returns
      -------
      Su : float
          Suratman number []
  
      Notes
      -----
      Also known as Laplace number. Used in two-phase flow, especially the 
      bubbly-slug regime. No confusion regarding the definition of this group 
      has been observed.
  
      .. math::
          \text{Su} = \frac{\text{Re}^2}{\text{We}} =\frac{\text{Inertia}\cdot
          \text{Surface tension} }{\text{(viscous forces)}^2}
  
      The oldest reference to this group found by the author is in 1963, from 
      [2]_.
  
      Examples
      --------
      >>> Suratman(1E-4, 1000., 1E-3, 1E-1)
      10000.0
  
      References
      ----------
      .. [1] Sen, Nilava. "Suratman Number in Bubble-to-Slug Flow Pattern 
         Transition under Microgravity." Acta Astronautica 65, no. 3-4 (August 
         2009): 423-28. doi:10.1016/j.actaastro.2009.02.013.
      .. [2] Catchpole, John P., and George. Fulford. "DIMENSIONLESS GROUPS." 
         Industrial & Engineering Chemistry 58, no. 3 (March 1, 1966): 46-60. 
         doi:10.1021/ie50675a012.
      '''
      return rho*sigma*L/(mu*mu)